Python Regular Expressions to implement string unescaping

Question

I am trying to implement string unescaping with Python regex and backreferences, and it doesn't seem to want to work very well. I'm sure it's something I'm doing wrong but I can't figure out what...

>>> import re
>>> mystring = r"This is \n a test \r"
>>> p = re.compile( "\\\\(\\S)" )
>>> p.sub( "\\1", mystring )
'This is n a test r'
>>> p.sub( "\\\\\\1", mystring )
'This is \\n a test \\r'
>>> p.sub( "\\\\1", mystring )
'This is \\1 a test \\1'

I'd like to replace \\[char] with \[char], but backreferences in Python don't appear to follow the same rules they do in every other implementation I've ever used. Could someone shed some light?

Answer 1

Isn't that what Anders' second example does?

In 2.5 there's also a string-escape encoding you can apply:

>>> mystring = r"This is \n a test \r"
>>> mystring.decode('string-escape')
'This is \n a test \r'
>>> print mystring.decode('string-escape')
This is 
 a test 
>>>